(1) Field of the Invention
This invention relates to a light-radiant heating furnace.
(2) Description of the Prior Art
Among a variety of apparatus adapted generally to carry out heat treatments therein, light-radiant heating furnace in which light radiated from a lamp or lamps is irradiated onto objects or materials to be treated (hereinafter referred to merely as "objects") for their heat treatment have following characteristic merits:
(1) Owing to an extremely small heat capacity of each lamp per se, it is possible to raise or lower heating temperature promptly;
(2) Since they feature indirect heating by virtue of light radiated from their lamps which are not brought into contact with objects, the objects are protected from contamination;
(3) They enjoy less energy consumption because full-radiation-state operations of the lamps are feasible in short time periods after turning the lamps on and energy efficiencies of the lamps are high; and
(4) They are relatively small in size and low in manufacturing costs compared with conventional resistive furnaces or high-frequency heating furnaces.
Such light-radiant heating furnaces have been used for heat treatment and drying of steel materials and the like and molding of plastics as well as in thermal characteristics testing apparatus and the like. Use of light-radiant furnaces have, particularly recently, been contemplated to replace the conventionally-employed resistive furnaces and high-frequency heating furnaces for carrying out certain semiconductor fabrication processes which require heating, for example, diffusion processes of dopant atoms, chemical vapor deposition processes, healing processes for crystal defects in ion-implanted layers, thermal treatment processes for electrial activation, and thermal processes for nitrifying or oxidizing surfaces of silicon wafers. As reasons for the above move, may be mentioned such advantages of light-radiant heating furnaces that objects under heat treatment are free from contamination, their electric properties are not deleteriously affected and the light-radiant heating furnaces require less power consumption.
Light-radiant heating furnaces have a variety of such advantages as mentioned above and have found wide-spread commercial utility in industry. Conventional light-radiant heating furnaces are however accompanied by a drawback that they are unable to heat objects uniformly to desired high temperatures in their entirety. Namely, a lamp has a sealed envelope made of silica glass or the like and forms a point light source or a line light source. It is thus unable to form any plane light source extending two-dimensionally, when used singly. Thus, it cannot heat an object uniformly to a desired high temperature in its entirety although it may be able to heat a part of the object uniformly.